This invention relates to a process and apparatus for the continuous preparation of polycarbonates by an interfacial process.
Polycarbonates derived from substituted bisphenols such as halogenated bisphenols are useful materials combining unique physical properties with the flame retardant behavior common to halogenated polycarbonates. For example, membranes made from high molecular weight tetrabromobisphenol A polycarbonate have shown high selectivity for the separation of mixtures of oxygen and nitrogen gases. Tetrabromobisphenol A polycarbonate has been shown to serve as a flame retardant material as well.
In making endcapped polycarbonates from substituted bisphenols such as halogenated bisphenols via an interfacial process, it is desirable to minimize the amount of residual monomer, endcapping agent and by-product diarylcarbonate in the product polycarbonate.
The presence of excessive amounts of residual monomer, endcapping agent or by-product diarylcarbonate in the product polycarbonate is undesirable since when a polycarbonate containing said residual monomer, endcapping agent or by-product diarylcarbonate is subjected to melt processing, as in a molding step, molding cycle times tend to be increased thereby reducing the molding equipment efficiency. Halogenated bisphenol derived polycarbonates containing significant levels of residual monomer, endcapping agent or by-product diarylcarbonate require longer molding cycle times compared with halogenated bisphenol derived polycarbonates that are substantially free of said residual monomer, endcapping agent and diarylcarbonates. Further, because residual monomer, endcapping agent and by-product diarylcarbonate tend to migrate to the polymer surface, the presence of said residual monomer, endcapping agent or by-product diarylcarbonate in a polycarbonate can lead to undesirable effects, such as xe2x80x9cplate outxe2x80x9d during molding operations. The low molecular weight species present in the polycarbonate from previous molding cycles are deposited on the mold surfaces. The presence of said low molecular weight species on the mold surfaces leads to blemishes in subsequently molded articles. Further, volatile residual monomers, endcapping agents and diarylcarbonates when present in a polycarbonate undergoing extruder melt processing have a tendency to condense and plug extruder vent lines thereby necessitating more frequent maintenance than would otherwise be required and resulting in equipment outages.
It would be desirable to develop a continuous interfacial process for the conversion of substituted bisphenols such as halogenated bisphenols directly into endcapped polycarbonates in a continuous manner while minimizing the presence of residual monomer, endcapping agent and by-product diarylcarbonate in the product polycarbonate. In addition, it would be desirable to develop a continuous interfacial process involving relatively short reactant residence times in the reactor system, and making efficient use of phosgene to produce endcapped polycarbonate oligomers of halogenated bisphenols having low levels of residual monomer, endcapping agent and by-product diarylcarbonate.
The present invention addresses these problems, and provides further surprising properties. These and further objects of the invention will be more readily appreciated when considering the following disclosure and appended claims.
In one aspect the present invention relates to a continuous process for the preparation of polycarbonate comprising the following steps:
Step (A) introducing into a continuous reactor system phosgene, at least one solvent, at least one bisphenol, caustic, and optionally one or more catalysts, thereby forming a flowing reaction mixture; said phosgene, solvent, bisphenol, caustic, and catalyst being introduced as components of at least 2 feed streams;
Step (B) passing the flowing reaction mixture formed in Step (A) through said continuous reactor system until substantially all of the phosgene has been consumed;
Step (C) introducing into said flowing reaction mixture in which substantially all of the phosgene has been consumed, caustic, at least one endcapping agent, optionally one or more solvents, and at least one catalyst; said caustic, endcapping agent, solvent and catalyst being introduced as one or more feed streams; and
Step D) allowing the reaction mixture formed in steps (A)-(C) to react to form a product polycarbonate and continuously removing said product polycarbonate from the continuous reactor system.
The present invention further relates to a continuous process for the production of endcapped oligomeric polycarbonates of substituted bisphenols, such as halogenated bisphenols, in which one or more bisphenols is converted in a continuous manner into a mixture comprising a bisphenol monochloroformate, and a bisphenol bischloroformate, said mixture of bisphenol chloroformates being converted in a continuous manner into endcapped oligomeric polycarbonate.